1. Field of the Invention
This invention relates to clearance of mines from the seabed and in particular from regions of the seabed close to the shoreline which have been mined to deter or prevent amphibious landings on the beach by amphibious landing craft.
2. Background of Prior Art
The problems of mine clearance of shallow water/beach areas for amphibious landings are well known. If it were possible for invaders to always have the choice of an ideal landing area, they would probably choose a comparatively gently sloping beach free from obstacles and composed of sand or shingle. The defenders will employ whatever defensive measures are open to them part of which will be the xe2x80x9csurf zonexe2x80x9d (SZ) which is suitable for xe2x80x9cvery shallow water miningxe2x80x9d (VSWM). The deployment of a mix of comparatively small contact, pressure, and influence mines sown in the SZ and VSWM areas means that many will become buried by the action or tide and wave action. In fact some mines are deliberately shaped to aid the burying process. Any invader will therefore need to clear a safe passage through such areas in order for effective landings to take place. Current techniques which attempt to achieve the foregoing appear to be both expensive and time consuming to apply, embracing as they do the step by step procedures now applied, e.g.:
(a) first locate the mines then
(b) neutralise or destroy them
The current means of implementing involve the use the highly expensive and complicated Mine Hunting Vessels (MHVs), robots, swimming teams and underwater vehicles, both manned and unmanned, and even in certain situations, trained dolphins.
It is now proposed that the means outlined in paragraphs (a) and (b) above should be dispensed with and in accordance with this invention, clearing the mines should be effected by directed large volumes of low velocity water at the seabed in a controlled manner, thereby clearing/excavating sand, shingle, cobbles and mines by rolling/water blasting them away, thus creating the safe passage needed.
Thus the invention provides a vessel having means at the bow of the vessel to direct a water flow ahead of the vessel downwardly towards the sea bed in front of and to either side of the path of the vessel to displace material from the sea bed including any weapon system or obstacles on or buried in the sea bed away from the path of the vessel.
The means for directing the water flow from the vessel will be referred to hereinafter as a water plough.
There are two main factors involved in achieving the foregoing:
(a) The effective clearance distance of the water
The distance at which the water, when discharged from the water plough, will effect the necessary scouring/clearing of the seabed, and therefore the objects embedded in it, e.g. stones, rocks, mines etc.
(b) The damage radius of the mine
The effective damage radius of any mine which may explode as they are being swept away. This will vary according to:
(i) the type and amount of explosive contained, and
(ii) the depth of water in which it sits, e.g. in very shallow water the explosion will take the path of least resistance, and the direction will therefore mostly be towards the surface.
Devices already exist for which it is claimed that a six ft. diameter shrouded propeller, which requires 250-500 HP only can move seabed material at the following rates:
This at a distance of some five to ten yards and furthermore clearing/excavating down to a depth of some 3 ft. or so, below the surface of the seabed.
The best information gathered so far, and this is very much xe2x80x98rule of thumbxe2x80x99 regarding the volume of influence of underwater explosions, is that a 1000 lbs charge has a damage radius of some 50 yds. Whilst the amount of explosive required to double the volume of influence can be:
(a) as high as 10 times the amount of explosive, or
(b) as little as 4 times the amount
However if it is accepted that 20 lbs of explosive (abut the charge in some anti invasion mines), would have a damage radius of say 10 to 12 yds, then a properly constructed Water Plough should be able to clear those mines, without its function being irreparably impaired, by those that do explode.
There are various ways in which the xe2x80x98scouring waterxe2x80x99 action could be produced, ranging from:
(a) reversing the thrust from the ships propellers
(b) by specially constructed ships, e.g. utilizing/directing the prop wash from say, bow thrusters, this by positioning devices to turn the prop wash through 90% so that it blows the clear path required ahead of the ship
(c) by attaching a large fabricated intake to the bow of the ship, which accepts water and turns it through 90xc2x0 to a narrowed projecting outlet thereby forcing a xe2x80x98wavexe2x80x99 ahead of the vessel and creating the necessary turbulence/scouring action
(d) by the use of low pressure pumps with a large volumetric output
(e) captive propellers in a xe2x80x98caged enclosurexe2x80x99, with power being supplied from the ships systems
(f) by contra rotating paddles
(g) using high speed water jets to product a Coanda effect to get the volume of water required flowing in the desired direction.
The water plough should be constructed in such a manner, that the wave effect it produces should:
(a) create the scouring/cleaning effect at least 10 yds, ahead of its outlet, it should additionally
(b) be constructed in flexiblexe2x80x94resilient material, so designed as to direct the water flow in the desired direction but also to allow activation by a sensor which would react to the pressure impulse/shock wave created by an exploding mine and cause the Water Plough to:
(i) swing up
(ii) swing openxe2x80x94away
(iii) recoil, from the xe2x80x98pressurexe2x80x99 created
(c) traverse through 180xc2x0 around the bow of the vessel
(d) be mounted on a boom (e.g. 90 ft in length), thereby sweeping a wide channel (of 180 ft for a 90 ft boom) as the vessel approaches the landing area.